Regulation of PDGF-stimulated SHIP2 tyrosine phosphorylation and association with Shc in 3T3-L1 preadipocytes.

Ottawa Health Research Institute, Department of Medicine, University of Ottawa, Ottawa, Ontario, Canada.
Journal of Cellular Physiology (Impact Factor: 3.87). 07/2007; 211(3):598-607. DOI: 10.1002/jcp.20965
Source: PubMed

ABSTRACT In 3T3-L1 and human preadipocytes, insulin results in the isolated rise in phosphatidylinositol (PI)-3,4,5-P3, whereas PDGF produces PI(3,4)P2 in addition to PI(3,4,5)P3. SH2 domain-containing inositol 5-phosphatase 2 (SHIP2) converts PI(3,4,5)P3 into PI(3,4)P2. PDGF, but not insulin, stimulates SHIP2 tyrosine phosphorylation and its association with Shc in human and 3T3-L1 preadipocytes. We now demonstrate that SHIP2 tyrosine phosphorylation and association with Shc in PDGF-treated 3T3-L1 preadipocytes was reduced by bisindolylmaleimide I (BisI), an inhibitor of conventional/novel protein kinase C (PKC). However, the production of PI(3,4)P2 and PI(3,4,5)P3 by PDGF was unaffected by BisI. Activation of PKC by 12-O-tetradecanoylphorbol-13-acetate (TPA) was not sufficient to induce SHIP2 tyrosine phosphorylation. Furthermore, we identified threonine 958 (T958) as a novel PDGF-responsive SHIP2 phosphorylation site. Mutation of T958 to alanine reduced PDGF-stimulated SHIP2 tyrosine phosphorylation and association with Shc, but did not alter its anti-proliferative effect on preadipocytes. This study demonstrates that SHIP2 tyrosine phosphorylation and Shc association can be regulated by serine/threonine signaling pathways, either indirectly (via PKC), or directly (via T958). Interestingly, the anti-proliferative effect of SHIP2 T958A, as well as another SHIP2 mutant (Y986F, Y987F) that also displays defective tyrosine phosphorylation and Shc association, does not depend on these molecular events.

  • [Show abstract] [Hide abstract]
    ABSTRACT: The Src homology 2 domain-containing inositol 5'-phosphatase 1 (SHIP1) dephosphorylates phosphatidylinositol 3,4,5-trisphosphate to phophatidylinositol 3,4-bisphosphate in hematopoietic cells to regulate multiple cell signaling pathways. SHIP1 can be phosphorylated by the cyclic AMP-dependent protein kinase (PKA), resulting in an increase in SHIP1 activity (Zhang, J., Walk, S. F., Ravichandran, K. S., and Garrison, J. C. (2009) J. Biol. Chem. 284, 20070-20078). Using a combination of approaches, we identified the serine residue regulating SHIP1 activity. After mass spectrometric identification of 17 serine and threonine residues on SHIP1 as being phosphorylated by PKA in vitro, studies with truncation mutants of SHIP1 narrowed the phosphorylation site to the catalytic region between residues 400 and 866. Of the two candidate phosphorylation sites located in this region (Ser(440) and Ser(774)), only mutation of Ser(440) to Ala abolished the ability of PKA to phosphorylate the purified, catalytic domain of SHIP1 (residues 401-866). Mutation of Ser(440) to Ala in full-length SHIP1 abrogated the ability of PKA to increase the activity of SHIP1 in mammalian cells. Using flow cytometry, we found that the PKA activator, Sp-adenosine 3',5'-cyclic monophosphorothioate triethylammonium salt hydrate (Sp-cAMPS) blunted the phosphorylation of Akt downstream of B cell antigen receptor engagement in SHIP1-null DT40 B lymphocytes expressing native mouse SHIP1. The inhibitory effect of Sp-cAMPS was absent in cells expressing the S440A mutant of SHIP1. These results suggest that activation of SHIP1 by PKA via phosphorylation on Ser(440) is an important regulatory event in hematopoietic cells.
    Journal of Biological Chemistry 11/2010; 285(45):34839-49. · 4.60 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Obesity is a well-recognized cancer risk factor. The increase in risk for colorectal, endometrial, breast and eso-phageal cancers associated with obesity ranges from 1.5-to as much as 3-fold. Obese patients develop more aggressive cancers that are less responsive to treatment. Here, we review the available data on an obesity-linked gene, SH2-domain-containing inositol 5-phosphatase-2 (SHIP2), in light of new experimental and clinical evidence of its pro-oncogenic role. A putative diabetes drug target, SHIP2 is an important negative regulator of insulin signaling that acts downstream of phosphoinositide 3-kinase (PI3-kinase). In mice, SHIP2 levels are increased by a high-fat diet, and its knockout prevents diet-induced obesity. Taking together these findings, we propose that SHIP2 is a potential anti-cancer target with a high therapeutic index owing to its cancer-specific overexpression and/or differential function combined with the absence of major untoward effects upon its loss of function in normal cells. We compare and contrast the pro-oncogenic function of SHIP2 with the current understanding of cancer-relevant functions of PTEN and PTP-1B, two negative regulators of insu-lin function. The provocative idea that a negative regulator of insulin function will positively influence oncogenesis pre-sents the intriguing possibility that its inhibition will be a beneficial strategy for two major therapeutic areas: metabolic diseases (such as obesity and diabetes) and cancer.
    Current Cancer Therapy Reviews 05/2009; 5(2).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Phosphoinositide (PI) phosphatases such as the SH2 domain-containing inositol 5-phosphatases 1/2 (SHIP1 and 2) are important signalling enzymes in human physiopathology. SHIP1/2 interact with a large number of immune and growth factor receptors. Tyrosine phosphorylation of SHIP1/2 has been considered to be the determining regulatory modification. However, here we present a hypothesis, based on recent key publications, highlighting the determining role of Ser/Thr phosphorylation in regulating several key properties of SHIP1/2. Since a subunit of the Ser/Thr phosphatase PP2A has been shown to interact with SHIP2, a putative mechanism for reversing SHIP2 Ser/Thr phosphorylation can be anticipated. PI phosphatases are potential target molecules in human diseases, particularly, but not exclusively, in cancer and diabetes. Therefore, this novel regulatory mechanism deserves further attention in the hunt for discovering novel or complementary therapeutic strategies. This mechanism may be more broadly involved in regulating PI signalling in the case of synaptojanin1 or the phosphatase, tensin homolog, deleted on chromosome TEN.
    BioEssays 05/2012; 34(8):634-42. · 4.84 Impact Factor